1. Field of the Invention
The present invention relates to a vibration wave actuator and a system using the vibration wave actuator as a driving source.
2. Related Background Art
Rod-shaped ultrasonic wave motors have already been described in, e.g., Japanese Laid-Open Patent Application Nos. 3-40767, 3-289375, and the like. FIG. 13 is an exploded perspective view of a rod-shaped ultrasonic wave vibration member, and FIG. 14 is a longitudinal sectional view of a rod-shaped ultrasonic wave motor.
In the vibration member shown in FIG. 13, a driving A-phase piezoelectric member al consisting of a group of two piezoelectric members PZT1 and PZT2, a driving B-phase piezoelectric member a2 consisting of a group of two piezoelectric members PZT3 and PZT4, and a sensor piezoelectric member S1 consisting of a single piezoelectric member are stacked (laminated), as shown in FIG. 13, and electrode plates A1 and A2 for supplying a driving voltage signal and an electrode plate S for outputting a sensor signal are arranged among these piezoelectric members, as shown. In addition to these electrodes, GND (ground) electrode plates G1, G2, and G3 are arranged to apply a GND potential. Metal blocks b1 and b2 which consist of, e.g., brass, stainless steel, or the like and have relatively small vibration attenuation are arranged before and after these piezoelectric members and electrode plates to clamp them. By fastening the metal blocks b1 and b2 using a fastening bolt c, the piezoelectric members and electrode plates are integrated, and a compression stress is applied to the piezoelectric members. At this time, in order to use only one sensor piezoelectric member S1, an insulating sheet d is arranged between the fastening bolt c and the metal block b2.
Note that wires and the like are attached to projecting portions (tabs) of the electrode plates by soldering, and are connected to a driving circuit (not shown).
At this time, the A- and B-phase piezoelectric members a1 and a2 are arranged to have an angular positional shift of .pi./2 rad therebetween. When these piezoelectric members excite bending vibrations in two orthogonal in-plane directions including the axis of the vibration member to provide an appropriate time phase difference therebetween, the surface particles of the vibration member move in a circular or elliptic motion, thereby frictionally driving a movable member pressed against the upper portion of the vibration member.
FIG. 14 shows an example wherein such a vibration member is used in a rod-shaped ultrasonic wave motor. In this example, the fastening bolt c of the vibration member includes a small-diameter support column portion c2 at its distal end portion, so that a fixing member g fixed to the distal end portion of the support column portion c2 can be fixed to the motor itself. The fastening bolt c also serves to rotatably support a rotor r, and the like. The rotor r contacts the distal end portion of the metal block b1, and is compressed by pressing a coil spring h in a spring case i from the fixing member g via a bearing member e and a gear f.
The piezoelectric members used in this rod-shaped ultrasonic wave motor will be described in more detail below. Each of the piezoelectric members PZT1 to PZT4 as independent members is formed as follows. That is, as shown in FIG. 15, a piezoelectric ceramic 200 prepared by compacting and sintering a powder is machined into a disk shape having a diameter of 10 mm, and the two surfaces of the disk are lapped to obtain a disk thickness of 0.5 mm. Two almost semi-circular divided electrode films 202-1 and 202-2 are formed via a slit 201 on the upper surface of the disk, and an electrode film 203 is formed on the entire lower surface. Thereafter, the semi-circular electrode films 202-1 and 202-2 are polarized to have different directions of polarization (+) and (-) respectively, thus providing piezoelectric characteristics. When such piezoelectric members are assembled like the A-phase piezoelectric member a1 shown in FIG. 13, the piezoelectric members PZT1 and PZT2 are stacked to sandwich the electrode plate A1 therebetween, so that portions having the same polarization face each other (arrows 205 indicate the direction of polarization), and at the same time, the slits overlap each other, as shown in FIGS. 16A and 16B.
Also, the GND electrode plates G1 and G2 are vertically stacked. In this state, when a driving AC voltage is applied to the electrode plate A1, since the right and left portions of the piezoelectric members PZT1 and PZT2 in FIGS. 16A and 16B have different polarization characteristics, if one expands, the other contracts, and this operation is alternately repeated, thus generating a bending vibration in the vibration member. Note that the B-phase piezoelectric member generates a bending vibration in substantially the same state as in the A-phase piezoelectric member, except that the direction of the slit is different by .pi./2 rad from that of the A-phase piezoelectric member.
However, in the above-mentioned prior art, since each piezoelectric member is manufactured by compacting and sintering a powder, performing machining, and then performing polarization processing after the electrodes are formed, the manufacture of each piezoelectric member requires much time and cost.
In consideration of handling upon machining and polarization processing of the piezoelectric member, and assembling of the vibration member, the thickness of the piezoelectric ceramic member cannot be rendered very thin because of the required mechanical strength. As a result, when the number of layers of piezoelectric members is to be further increased, a multi-layered piezoelectric member portion undesirably has a large size, and inhibits the manufacture of a compact ultrasonic wave motor having a diameter equal to or smaller than a pencil. In addition, the above-mentioned manufacturing process makes an increase in output and a decrease in driving voltage of the ultrasonic wave motor, which would be achieved by such a multi-layered structure, difficult to achieve.
As can be understood from the description of the prior art, upon assembling of the vibration member, a large number of piezoelectric members and a large number of electrode plates are alternately stacked, and thereafter, wires are attached to the end portions of the electrode plates by soldering. As a result, the assembling process requires much time, and the reliability of assembling is not satisfactory.
On the other hand, as disclosed in Japanese Patent Publication No. 1-17354, and the like, a conventional ring-shaped or disk-shaped ultrasonic wave motor has a vibration member in which electrostrictive elements or piezoelectric members are fixed to an elastic member of, e.g., a metal, which has low vibration attenuation characteristics. A movable member (contact member) is arranged in press contact with the surface of the elastic member. High-frequency voltage signals having a time phase difference therebetween are applied to the electrodes of juxtaposed electrostrictive elements or piezoelectric members, thereby (relatively) driving the movable member (contact member).
On each piezoelectric member used in this vibration member, a large number of divided electrodes are formed on one surface, and a whole-surface electrode is formed on the other surface which is joined to the elastic member. The plurality of electrodes on one surface constitute electrode groups corresponding to a plurality of phases, i.e., two, A and B phases subjected to driving signals. These electrode groups corresponding to the two phases are arranged at intervals corresponding to a 1/4 wavelength or an odd-numbered multiple of the 1/4 wavelength. A plurality of piezoelectric members of each group, which are subjected to polarization processing in different directions have an interval of a 1/2 wavelength therebetween. When a high-frequency voltage signal is applied to the piezoelectric members of each group having different directions of polarization, a vibration for one wavelength is excited. When a plurality of groups of piezoelectric members are prepared, standing waves having a wave number corresponding to the number of groups are formed, and as a result, a travelling wave having one or plural wave number is excited in the vibration member.
However, since the conventional electrostrictive element or piezoelectric member has a single-layered structure, high-frequency voltages of several ten volts must be applied to drive an ultrasonic wave motor using the piezoelectric members to obtain a practical output, the voltage of a battery as a power supply of a portable equipment such as a camera is insufficient, and a booster circuit must be prepared.
Note that a stack-type ceramic actuator which uses piezoelectric members constituted by stacking piezoelectric member plates is known [Kenji Uchino, "Piezoelectric/electrostrictive Actuator", Kyoritsu Press]. In this actuator, piezoelectric members with simple directions of polarization are merely stacked. However, when piezoelectric member plates having a complicated structure in which a large number of divided electrodes are formed and stacked with alternating directions of polarization, wiring lines for applying polarization processing and driving signals are complicated, and it is impossible to realize such an actuator.